Analyzing samples with dilute components can be a useful technique in analytical chemistry, medical science, and other technology fields. However, separating or even detecting components with low concentrations can be challenging. For example, cardiac troponin I (cTnI) is a biomarker useful for diagnosing patients for myocardial injury. In particular, it is believed that a ratio between phosphorylated and unphosphorylated cTnI can be a good indicator of a patient's risk of suffering myocardial damage.
However, cTnI levels in healthy people are often lower than detection limits of conventional diagnostic techniques. Though assays (e.g., i-STAT provided by Abbott Diagnostics of Abbott Park, Ill.) have been developed to detect cTnI, such assays can only measure total cTnI content and do not distinguish between phosphorylated and unphosphorylated cTnI. Other conventional analysis techniques for cTnI include non-equilibrium isoelectric focusing, mass spectrometry, and phosphate-affinity sodium dodecyl sulfate polyacrylamide gel electrophoresis (“SDS-PAGE”). These techniques, however, have long test time and low sample throughput.